1. Field of Invention
The invention relates to a fiber laser.
2. Related Art
Fiber laser, due to its advantages such as high stability, small size, portability and easy installation, plays an important role in the fields of optical communication, spectrum measurement and optical analysis. Besides, fiber laser has very high slope efficiency and optical power output, so it has become a widely applied laser system in industries.
Ultrashort pulse laser (also referred to ultrafast laser) usually means the pulse laser with the pulse duration being of the order of a picosecond (10-12) or less. The widely applied ultrafast laser currently is the Ti:Sapphire mode-locked laser and its derivative technology with a wavelength range from 700 to 900 nanometers, a pulse duration of about 100 femtoseconds (10-13), a repetition rate of about 80 MHz and a peak power up to 10 KW or more. As to the pulse duration, energy and operating stability of the ultrafast laser, they are good enough to induce a nonlinear effect and thus can be applied to the microscopic technology, bringing out various applications.
The optical fiber doped with ytterbium (Yb) is a gain medium and is widely researched recently due to its broad gain bandwidth, high saturation intensity and high slope efficiency. Besides, the mode-locked method can be used to further reduce the laser pulse duration to the order of a picosecond to femtosecond. The mode-locked method includes active mode locking, passive mode locking, synchronously pumped mode locking, self mode locking and colliding mode locking.
Besides, more and more researches are done for the noise-like pulse of the fiber laser, which has a higher pulse power and a narrower peak in spectrum and is thus suitable for a long-distance transmission without the distortion. Furthermore, due to its broader bandwidth, more information can be carried during the detection or transmission. So, more and more researchers contribute themselves to the topic of noise-like pulses.
However, the center frequency and the bandwidth of the pulse laser generated by the fiber laser are fixed and can not be adjusted at liberty, so that the applicability thereof is reduced. Therefore, it is an important subject to provide a fiber laser that can generate high-power pulse laser and the center frequency and bandwidth of the generated pulse can be adjusted.